\vskip10pt
\begin{figure}[hbt]
\begin{center}
 \includegraphics[width=.9\textwidth]{chapter2/chapter2_6}
\caption{Examples of usage scenarios for fixed (F-Rs), nomadic (N-RS), and mobile stations (M-RS) [3]}
\label{fig:chapter2_6}
\end{center}
\end{figure}